This invention relates to gas turbine combustors; and, in particular, to fuel nozzles for gas turbine combustors; igniters for igniting a fuel/air mixture; and, catalyst material for the inhibition of NOx formation by promoting complete combustion at reduced flame temperature.
Gas turbine manufacturers are currently involved in research and engineering programs to produce new gas turbines which will operate at high efficiency without producing undesireable air polluting emissions. The primary air polluting emissions usually produced by gas turbines burning conventional fuels are oxides of nitrogen, carbon monoxide and unburned hydrocarbons. A combustion catalyst can be used in the reaction zone of a gas turbine combustion system to promote complete combustion of lean premixed fuel and air which will minimize the level of these air polluting emissions. Combustion catalyst designed and manufactured with current state-of-the-art technology are not capable of operation at gas turbine ignition and low load conditions using natural gas or most conventional turbine fuels due to the relatively low combustor inlet temperature and temperature rise associated with these operating conditions.
One method of obtaining a satisfactory catalytic combustion system for gas turbine operation at ignition and low load operation is to supplement the catalytic reactor with a more conventional diffusion preburner at these conditions. The preburner allows for ignition and flame stabilization prior to the addition of the main fuel. In order to minimize air pollution emissions from this diffusion flame preburner, protect the catalytic reactor and provide operational flexibility for the catalytic combustion system, it is necessary for the diffusion flame preburner to have the capability of igniting and/or operating at extremely low fuel flow/heat release rates and very lean overall fuel/air mixtures. It is the intent of this invention to extend the operating range of a heavy-duty industrial gas turbine diffusion flame combustion system to extremely lean overall fuel/air mixtures and fuel flow/heat release rates so low that blow-out would occur with a conventional combustor. It is also the intent of this invention to achieve combustion system ignition at conditions of fuel flow and overall fuel air mixture strength which are too low/lean to obtain ignition with a conventional heavy-duty industrial gas turbine combustion system and spark igniter.
Standard practice for heavy-duty industrial gas turbine combustion systems is to obtain ignition using an electrical discharge (spark) igniter and to stabilizer the diffusion flame aerodynamically. Once ignition is established, no external energy source (i.e., other than combustion of the primary fuel) is required. Alternative ignition means, such as torch igniters are available, however, glow plugs are not in use since simpler systems will suffice for conventional combustion.
It is an object of this invention to provide a fuel nozzle and ignition system for a gas turbine combustor which is capable of igniting fuel at low fuel flow and very lean overall fuel/air mixtures.
It is a further object of this invention to extend the operating range of a gas turbine combustor with respect to the potential for blow-out by providing a fuel nozzle and ignition system in accordance with the present invention.
It is still another object of this invention to minimize the formation of NOx at low fuel flow/heat release conditions and very lean overall fuel/air mixture.
The novel features believed characteristic of the present invention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof may best be understood with reference to the following description and drawings.